Method of making magnets

ABSTRACT

A method of making magnets of small size which comprises depositing magnet material in apertures of controlled size in a sheet of material of desired thickness, applying electromagnetic forces to magnetically orient the particles of magnet material, applying pressure to the deposits of magnet material to produce densification thereof, and sintering.

United States Patent Reid July 1, 1975 [54] METHOD OF MAKING MAGNETS3,505,139 4/!970 Wentworth 264/DIG. 58

[75] Inventor: William R. Reid, Wollaston, Mass. 73 Assigneez RaytheonCompany, Lexington, 3,655,464 4/l972 Benz .4 l48/IO3 Mass 3,662,3575/l972 Enoch.. l48/l08 3,672,867 6/l972 Little 148/[05 [22] Filed: Sept.1, 1971 Primary Examiner-Walter R. Satterfield [21] Appl' No" 177,025Attorney, Agent, or FirmHarold A. Murphy; Joseph D. Pannone; John T.Meaney [52] US. Cl. 148/108; 29/608; 148/105;

[51] Int. Cl. CZID 1/04 58 Field of Search l48/l0l, 103, 105, I08;Afnethod {nakmg magnets S118 Whlch 264/24, 319 D10 58; 29/608, 604' 580'prises depositing magnet material in apertures of con- 530' DEL 31trolled size in a sheet of material of desired thickness, applyingelectromagnetic forces to magnetically orient [56] References Cited thegarticles off magnet materiall, applytiing prjssurte to t e e osits 0 manet materia to pro uce ensi ICH- UNITED STATES PATENTS tion thzreof, andsiitering. 3,274,303 9/l966 Miiller 264/3l9 3,333,334 8/1967Kuliczkowski et al ..,..f 29/608 1 Claim, 7 Drawing Figures METHOD OFMAKING MAGNETS BACKGROUND OF THE INVENTION In the production of magnets.it has been found very difficult and expensive to produce small magnetsor micromagnets in large quantities and of relatively uniform size. Itwill be understood that in the manufacture of devices such as hearingaids. timepieces, reed switches and magnetic pickups, for example. thatthe magnets in the devices should be not only of satisfactory qualitybut also should be consistently of desired relatively uniform sizes andshapes. In many cases it has been the practice to produce small magnetsby first making large magnets by conventional methods and subsequentlycutting or breaking up the large magnets into the micromagnets ofdesired sizes and shapes. In addition to the initial fabrication expenseand effort involved in initially making the large magnets. there also isincurred the added expense and effort in reducing the large magnets tomicro sizes. thereby increasing the overall production costs tounwarranted levels. Furthermore, such methods often preclude thepossibility of producing large quantities of micromagnets which arerelatively uniform in size and shape.

SUMMARY OF THE INVENTION The above and other disadvantages of prior artmethods or processes for making small magnets are overcome in the methodof the present invention by the hereinafter described process stepswhich include first the production of a support having therein arelatively large number of apertures or cavities of a size and shapeconforming substantially to the diameter and shape of the magnets to beproduced. The support is of a material which will be compatible with themagnet materials to be subsequently utilized. that is, it should be of amaterial which will not contaminate the magnet materials duringsubsequent heat cycles.

This support is disposed upon a suitable flat surface such as one endsurface of an electromagnet. At this time the apertures or cavities inthe support are filled with particles of the selected magnet powder.With the electromagnet on, the powder particles will becomeautomatically magnetically oriented. The deposits of powder are thencompacted and densified in any appropriate manner. If relatively lowdensity is required such compaction may be achieved by means such assqueegee pressure. For high density magnets compaction may be achievedas by. for example. covering the surface or surfaces of the support witha selected thin sheet or film of flexible material such as rubber orplastic and then applying fluid to the film under pressure in a suitabledevice such as a hydraulic. hydrostatic or isostatic apparatus. Pressureupon the film will be translated to the magnet powder deposits whereuponthey will be compacted and densified as desired.

The support may then be transferred into a sintering furnace where heatis applied in the known manner. After sintering the resultant magnetswill be easily re movable from the support. Such magnets produced inthis manner have been found to be relatively uniform in size. shape andother characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of theinvention will become apparent from the following description taken inconnection with the accompanying drawings. wherein:

FIG. I is an isometric view of a magnet produced by the method of thisinvention;

FIG. 2 is an enlarged fragmentary isometric view partly in section ofone type of magnet support utilized in this invention;

FIG. 3 is an enlarged sectional view of the support shown in FIG. 2 withassociated elements used during a process of magnet manufacture;

FIG. 4 is an enlarged fragmentary side view of assembled elements of theapparatus;

FIG. 5 is an enlarged fragmentary sectional view illustrating a step inthe method of the invention;

FIG. 6 is a diagrammatic illustration of one form of magnet powdercompaction apparatus; and

FIG. 7 is an enlarged fragmentary view partly in section of a modifiedsupport utilizable in the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring more particularly tothe drawings wherein like characters of reference designate like partsthroughout the several views. there is shown in FIG. I a magnet I0 of atype which may be made by the method of this invention. Magnet 10 is ofextremely small size such as will permit its use in relatively smalldevices such as hearing aids. watches. magnetic pick ups, reed switches.meters or fuses. for example. and may be of any selected configuration.Magnet 10 in FIG. I for convenience is shown as disc shaped and is of adiameter and thickness which is conducive to the terminologymicromagnet." As an example. magnet 10 may be less than .078 inch indiameter and less than .020 inch in thickness. Obviously. making suchmicromagnets in large production quantities in an economical manner byconventional magnet making methods is undesirable for reasons ofeconomy. Furthermore. it is also difficult to make such desiredproduction quantities wherein the micromagnets will be substantiallyuniform from magnet to magnet as well as from batch to batch.

In accordance with this invention a magnetsupporting matrix 12 (FIG. 2)is provided in the form of a sheet or block of rigid material which willnot contaminate the magnet materials during processing. The support 12may be, for example, in the form of a sheet of molybdenum or iron. forexample. having any selected length and width suitable for use in theprocessing equipment. The thickness of the support sheet I2 issubstantially equal to or slightly greater than the thickness desired ofthe magnets being produced. For example. a moly sheet about .020 inchthick. 7 inches wide and 22 inches long has been found to beparticularly suitable for making approximately l5.000 magnets having adiameter of slightly less than .078 inch and a thickness of slightlyless than .020 inches.

The support is provided with a large number of holes. apertures orperforations 14 which. in the production of micromagnets of theexamplary size referred to above. are l5.000 in number and about .078inch in diameter.

The sheet support I2 is placed on the flat negatively polarized end ofan electromagnet 16 as illustrated in FIG. 6 and the electromagnet coilI8 is electrically energized. At this time the apertures or holes 14 inthe support are filled with powdered magnet material as shown in FIG. 3.

Since the magnets to be produced by the method of this invention may bepermanent magnets comprised of any selected materials. the particularmaterials comprising the powder 20 are not in themselves a part of thisinvention. However. a particularly good magnet material comprises apowder mixture containing cobalt and a rare earth such as samarium aloneor mixed with praseodymium. lanthanum or cerium where the samariumrepresents one-half or more of the total rare earth ingredient. Such amagnet composition is described in U.S. Pat. application Ser. No.|3l.777 filed Apr. (1. 1971 and assigned to the assignce of the presentinvention.

With the electromagnet l6 energized. the powder or domains of thedeposits 20 will become magnetically oriented so that the deposits willbe magnetically anisotropic. that is, they will have a preferreddirection of magnetization.

After any loose powder has been skimmed or brushed off the support T2the deposits 20 are compacted to the desired density. lf relatively lowdensity is satisfactory. compaction may be achieved by rolling asqueegee over the deposits. This may be done with or without theinterposition of a thin. flexible membrane. film or the like 22 over thesupport 12. Pressure should be at least in the order of 250 lbs.however. to render the deposits self-supporting during subsequenttransport of the support to other apparatus. as will be described.

When relatively high density is desired ofthe deposits 20. it becomesnecessary to apply greater pressures, This is done by laying a film 22over the support and deposits. inserting the assembly in a hydraulic orhydrostatic (isostatic) press 24. and operating the press so that itspiston 26 will urge a supply of water 28 or other selected fluid towardthe deposits 20. This pressure of fluid upon the film 22 will cause thefilm to assume the shape shown in FIG. 5 as the deposits becomecompacted and densified. Such apparatus will apply pres sures of as muchas about five tons per square inch.

lt is to be understood that the film 22 may be any suitable thinflexible material such as rubber or plastic. and that beneath thesupport 12 there may be interposed. if desired. a separate removablesheet 30 of rigid material as shown in FlGS. 3-5 to aid in supportingthe deposits 22 during transport of the support [2 and to aid in keepingthe surface of the electromagnet l6 clean.

After the compaction step the support 12 and compacted deposits 20 areplaced in a sintering furnace (not shown) where the deposits 20 aresintered. Any

suitable sintering furnace and method may be employed. For example.temperatures in the vicinity of about I.IOOC may be applied after whichthe deposits. which are now small magnets. may be easily cooled andremoved from the apertures 14 in the support 12. The magnets generallyneed no further processing but, if desired. may be further formed ormachined. They may also be again magnetized in the same magnet directionas employed during the initial compaction step. with or withoutreversing the magnetic poles.

It is to be understood that although a thin apertured sheetlike support12 has been described for use in supporting the deposits 22, a block 32of suitable benign material such as molybdenum or cast iron. forexample. may be provided in one surface 34 with a large number ofshallow recesses or depressions 36 having the sizes and shapes desiredof the magnets to be produced. The recesses 36 function just as theapertures 14 in the support 12.

it is also to be understood that other modifications and changes may bemade by those skilled in the art without departing from the spirit ofthe invention as expressed in the accompanying claims. Therefore. allmatter shown and described is to be interpreted as illus trative and notin a limiting sense.

I claim:

1. A method of making magnets of a size less than about .078 inch indiameter and less than about .020 inch in thickness comprising the stepsof forming a multitude of perforations of a size and shape correspondingto the size and shape of the magnets to be produced in a rigid sheet ofmaterial which will not contaminate the material of the magnets duringfabrication;

placing the perforated sheet on the negatively polarized end of anelectromagnet and electrically energizing the coil of the electromagnet;

filling said perforations with deposits of a powder mixture containingcobalt and samarium;

laying a flexible film over the sheet and deposits;

inserting the assembled sheet. deposits and film in a press;

applying fluid under pressure of up to 5 tons per square inch to thcfilm to compact the deposits thereunder while continuing to electricallyenergize the clectromagnet'.

placing the sheet and compacted deposits in a sintering furnace;

applying heat of about l.lU0C to the compacted deposits to sinter same;

and removing the resultant individual magnets from

1. A METHOD OF MAKING MAGNETS OF A SIZE LESS THAN ABOUT 0.78 INCH INDIAMETER AND LESS THAN ABOUT .020 INCH IN THICKNESS COMPRISING THE STEPSOF FORMING A MULTITUDE OF PERFORATIONS OF A SIZE AND SHAPE CORRESPONDINGTO THE SIZE AND SHAPE OF THE MAGNETS TO BE PRODUCED IN A RIGID SHEET OFMATERIAL WHICH WILL NOTCONTAMINATE THE MATERIAL OF THE MAGNETS DURINGFABRICATION, PLACING THE PERFORATED SHEET ON THE NEGATIVELY POLARIZEDEND OF AN ELECTROMAGNET AND ELECTRICALLY ENERGIZING THE COIL OF THEELECTROMAGNET, FILLING SAID PERFORATIONS WITH DEPOSIT OF A POWDERMIXTURE CONTAINING COBALT AND SAMARIUM, LAYING A FLEXIBLE FILM OVER THESHEET AND DEPOSITS, INSERTING THE ASSEMBLED SHEET, DEPOSITS AND FILM INA PRESS, APPLYING FLUID UNDER PRESSURE OF UP TO 5 TONS PER SQUARE INCHTO THE FILM TO COMPACT THE DEPOSITS THEREUNDER WHILE CONTINUING TOELECTRICALLY ENERGIZE THE ELECTROMAGNET, PLACING THE SHEET AND COMPACTEDDEPOSITS IN A SINTERING FURNACE, APPLYING HEAT OF ABOUT 1.100*C TO THECOMPACTED DEPOSITS TO SINTER SAME, AND REMOVING THE RESULTANT INDIVIDUALMAGNETS FROM THE SHEET.